(1) Field of the Invention
This invention relates to a polyurethane dispersion and emulsion as well as a sheet-like porous material and a production process thereof. More specifically, this invention is concerned with a polyurethane dispersion and emulsion, which allow to produce with high productivity a sheet-like porous material excellent in various properties such as mechanical properties and water vapor transmission characteristics. This invention also relates to such a sheet-like porous material and a process for producing the sheet-like porous material with high productivity.
(2) Description of the Prior Art
Numerous sheet-like porous polyurethane materials have been known to date. Various processes have conventionally been known for their production. These processes may be divided roughly into wet processes and dry processes.
Each of these two types of processes has both merits and demerits. From the standpoint of productivity, dry processes are superior. As such dry processes, there have been known those described, for example, in Japanese Patent Publication No. 4380/1973 published on Feb. 7, 1973 and assigned to Teijin Limited, Japanese Patent Publication No. 8742/1973 published on Mar. 17, 1973 and assigned to Teijin Limited, Japanese Patent Laid-Open No. 41063/1976 laid open on Apr. 6, 1976 and assigned to Teijin Cordley Limited, Japanese Patent Laid-Open No. 66961/1979 laid open on June 1, 1979 and assigned to Teijin Limited, and Japanese Patent Laid-Open No. 68498/1979 laid open on May 9, 1979 and assigned to Teijin Limited. These known processes can each provide sheet-like porous materials having excellent performance. In order to obtain products of excellent performance by these processes, it is indispensable to selectively evaporate an organic solvent and water, which are both contained in a polyurethane emulsion employed. A very stringent temperature control is therefore required for gelation and drying. Further, the gelation and drying step requires a relative long period of time, for example, 30 minutes to 1 hour, leading to a problem that the productivity is very low due to the gelation and drying step although the other steps can be performed continuously.
These known processes involve a still further problem that the preparation of a polyurethane emulsion is either impossible or difficult since a polyurethane dispersion employed for the preparation of the polyurethane emulsion has poor stability and is prone to gelation.
In order to improve the productivity, it has been strongly desired in the present field of art to enhance the stability of a polyurethane dispersion useful in the practice of such processes as described above and hence to develop a process which does not require stringent control of the temperature in the gelatinizing and drying step and like parameters and can complete the gelatinizing and drying step in 10 minutes, preferably, in several minutes.